Impact of oxygen bonding on the atomic structure and photoluminescence properties of Si-rich silicon nitride thin films J. Appl. Phys. 112, 073514 (2012) Electron spin resonance features of the Ge Pb1 dangling bond defect in condensation-grown (100)Si/SiO2/Si1−xGex/SiO2 heterostructures J. Appl. Phys. 112, 074501 (2012) Capacitance spectroscopy study of deep levels in Cl-implanted 4H-SiC J. Appl. Phys. 112, 063717 (2012) Investigation of defect levels in Cs2Hg6S7 single crystals by photoconductivity and photoluminescence spectroscopies J. Appl. Phys. 112, 063702 (2012) Flat bands near Fermi level of topological line defects on graphite A method to deduce energy distributions of defects in the band gap of a semiconductor by measuring the complex admittance of a junction is proposed. It consists of calculating the derivative of the junction capacitance with respect to the angular frequency of the ac signal corrected by a factor taking into account the band bending and the drop of the ac signal over the space charge region of the junction. Numerical modeling demonstrates that defect distributions in energy can be reconstructed by this method with high accuracy. Defect distributions of polycrystalline Cu͑In,Ga͒Se 2 thin films are determined by this method from temperature dependent admittance measurements on heterojunctions of Cu͑In,Ga͒Se 2 with ZnO that are used as efficient thin film solar cells.

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In this paper the Sn loss from thin films of the material system Cu-Zn-Sn-S and the subsystems Cu-Sn-S and Sn-S in high vacuum is investigated. A combination of in situ x-ray diffractometry and x-ray fluorescence ͑XRF͒ at a synchrotron light source allowed identifying phases, which tend to decompose and evaporate a Sn-containing compound. On the basis of the XRF results a quantification of the Sn loss from the films during annealing experiments is presented. It can be shown that the evaporation rate from the different phases decreases according to the order SnS → Cu 2 SnS 3 → Cu 4 SnS 4 → Cu 2 ZnSnS 4 . The phase SnS is assigned as the evaporating compound. The influence of an additional inert gas component on the Sn loss and on the formation of Cu 2 ZnSnS 4 thin films is discussed.

A series of Cu(In,Ga)Se2 (CIGS) thin film solar cells with differently prepared heterojunctions has been investigated by admittance spectroscopy, capacitance-voltage (CV) profiling, and temperature dependent current-voltage (IVT) measurements. The devices with different CdS buffer layer thicknesses, with an In2S3 buffer or with a Schottky barrier junction, all show the characteristic admittance step at shallow energies between 40 and 160 meV, which has often been referred to as the N1 defect. No correlation between the buffer layer thickness and the capacitance step is found. IVT measurements show that the dielectric relaxation frequency of charge carriers in the CdS layers is smaller than the N1-resonance frequency at low temperatures where the N1 step in admittance is observed. These results strongly contradict the common assignment of the N1 response to a donor defect at or close to the heterointerface. In contrast, an explanation for the N1 response is proposed, which relates the admittance step to a non-Ohmic back-contact acting as a second junction in the device. The model, which is substantiated with numerical device simulations, allows a unified explanation of characteristic admittance, CV, and IVT features commonly observed in CIGS solar cells.

We present a detailed study of admittance spectroscopy and deep level transient spectroscopy on CuInSe2/CdS/ZnO thin film solar cells. The admittance spectra reveal an emission from a distribution of hole traps centered at an activation energy of 280 meV and a shallower level with a sharp activation energy of ∼ 120 meV. After repetitive annealing of the device in air at 200 °C, the activation energy of the latter level increases continuously from 120 to 240 meV, while the 280 meV hole traps remain unaffected. Deep level transient spectroscopy with optical excitation reveals an emission of minority carriers with time constants comparable to those observed for the shallow level in admittance spectroscopy. The shift of the activation energy after annealing also occurs in deep level transient spectroscopy and ascertains that the emissions observed in both techniques have the same origin. The magnitude and continuous shift of the activation energy of the minority carrier emission indicates a distribution of levels in the vicinity of the CdS/CuInSe2 heterointerface. In the case of interface states, the activation energy deduced from admittance spectroscopy corresponds to the position of the electron quasi-Fermi level at the interface, pointing to an inversion of the carrier type at the absorber surface. Measurements with an applied dc bias indicate that the electron Fermi level is pinned at the interface.